Search

BackgroundCyclin-dependent kinase 5 (CDK5) is a multifunctional enzyme involved in neuronal development, maturation and survival. CDK5 activity is tightly regulated by association with regulatory proteins p35 and p39. Upon neuronal insults, increased intracellular calcium activates calpain, cleaving p35 into p25, which has a higher affinity for CDK5. p25 hyperactivates CDK5, initiating apoptotic cascades that lead to significant dopaminergic (DAergic) loss that can leads to neurodegenerative disorders, such as Parkinson’s disease (PD).ObjectiveThis study investigates hyperactivation of CDK5/p25 in the 6-hydroxydopamine (6-OHDA) rat model of PD and specific inhibition of CDK5/p25 by truncated peptide 5 (TP5). TP5 was investigated for amelioration of 6-OHDA induced behaviour impairments and significant protection of dopamine neurons through tyrosine hydroxylase (TH).Methods6-OHDA induced motor impairments and reduced TH. Motor assessments included locomotor activity, beam transversal, fixed speed rotarod and amphetamine-induced rotations. Immunohistochemistry investigated DAergic neurodegeneration using TH levels and immunoprecipitation and assay investigated CDK5 activity.ResultsPre-administration of TP5 maintained locomotor activity, preserved beam transversal scores, protected motor coordination and attenuated amphetamine induced rotations in 6-OHDA lesioned rats, all indicative of neuroprotection by TP5. 6-OHDA without pretreatment of TP increased CDK5 activation. CDK5 activity in TP5+6-OHDA animals was not significantly different from artificial cerebrospinal fluid (aCSF) treated sham surgery controls. Immunohistochemistry revealed significant TH protection within the substantia nigra (SN) of TP5 pretreated animals.Conclusions6-OHDA increases CDK5 activity. Hyperactive CDK5/p25 inhibition in the 6-OHDA model has neuroprotective capability, protecting against the development of a toxin-based induction of PD-like motor phenotypes and pathology. This supports CDK5/p25 specific inhibition as a target for further neuroprotective therapeutic development.

Type 2 diabetes mellitus (T2DM) is worldwide epidemic, which challenges the health of the public. The pathological hyperactivity of cyclin-dependent kinase 5 (Cdk5) contributes to the pathogenesis of T2DM. P5, a peptide derived from the Cdk5 activator p35, shows excellent performance as a Cdk5 activity inhibitor. However, its inhibitory effect and functional regulation on Cdk5 activity needs to be confirmed. In this study, we conjugated P5 with a fluorescein isothiocyanate (FITC) tag at the N-terminus and a TAT protein transduction domain, an 11-amino acid peptide, at the C-terminus to synthesize TFP5, which was used to inhibits Cdk5 activity. We then evaluated the efficiency of TFP5 in treating T2DM. We demonstrated that TFP5 effectively penetrated pancreatic β-cells, inhibited the pathological hyperactivity of Cdk5, enhanced insulin secretion, and protected penetrated pancreatic β-cells (MIN6 cells) from apoptosis in pancreatic tissues of db/db mice (type II diabetes mice). Furthermore, we found that TFP5 reduced inflammation in pancreatic islets by reducing the expression of inflammatory cytokines, including TGF-β1, TNF-α, and IL-1β. These data indicates that the TFP5 peptide is a promising candidate for T2DM treatment.

Parkinson's Disease (PD) is a chronic progressive neurodegenerative disease. Current treatments for PD are symptomatic and only increase striatal dopamine levels. Proactive neuroprotective approaches that slow the progression of PD and maintain appropriate dopamine neuron populations are needed to treat the disease. One suggested mechanism contributing to the pathology of PD involves the binding of cyclin-dependent kinase 5 (Cdk5) to p25, creating a hyperactivated complex to induce cell death. The objective of this study is to investigate the neuroprotective and neurorestorative properties of Truncated Peptide 5 (TP5), a derivative of the p35 activator involved in Cdk5 regulation, via the inhibition of Cdk5/p25 complex function.